1. Field of the Invention
The present invention relates to an information data recording/reproducing apparatus adapted to record and/or reproduce information data, such as a data recorder based on, for example, the ID-1 format.
2. Description of the Prior Art
A data recorder based on an ANSI ID-1 format (Third Draft, PROPOSED AMERICAN NATIONAL STANDARD 19 mm TYPE ID-1 INSTRUMENTATION DIGITAL CASSETTE FORMAT, X3B6/88-12 Project 592-D 1988-03-22) has been proposed to perform high-density recording of information.
In such a data recorder, error correction for the information data is effected by employing a product encoding notation with Reed-Solomon code and recording it on a magnetic tape. In a playback mode, any transmission error is thereby detected and corrected.
FIGS. 1-8 relate to this type of ID-1 data recorder, and will now be described.
FIG. 1 illustrates a typical recording pattern formed on a magnetic tape by a data recorder based on the ID-1 format. In this diagram, ANN identifies an annotation track for recording notes thereon, and data tracks TR1, TR2, TR3 and so forth record information data, wherein 1 sector is formed per data track. The data tracks are recorded alternately by heads with different azimuths. Further shown are a control track CTL for recording a control signal, and a time code track TC for recording a time code.
The content of each of the data tracks TR1, TR2, TR3, . . . is illustrated in FIG. 2. Specifically, one data track TR records one sector SEC and is constituted by a preamble PR, a data recording portion DT and a postamble PS. The preamble PR is recorded in the generally lower portion at the beginning of the oblique data track.
The preamble PR is comprised of a 20-byte ascending sequence RUS, a 4-byte sync code SYNC.sub.PR, 4-byte sector identification data ID.sub.SEC1, and 6-byte auxiliary data DT.sub.AUX, arranged as illustrated.
The adjacent data recording portion DT is comprised of 256 sync blocks BLK (BLK.sub.0, BLK.sub.1, BLK.sub.2, . . . BLK.sub.255) in which the information data is recorded. Each sync block BLK is formed of a 4-byte block sync code SYNC.sub.BLK, 1-byte block identification ID.sub.BLK data, 153-byte inner data DI (inner-coded input information data) and an 8-byte parity code RI based on Reed-Solomon code notation.
The further adjacent postamble PS is comprised of a 4-byte sync code SYNC.sub.PS and 4-byte sector identification data ID.sub.SEC2.
FIG. 3 shows a recording system in accordance with the ID-1 format. In this recording system, the input information data is recorded after being encoded for error correction by product code notation.
The operation of the recording system is performed in the following manner. 8-bit (1-byte) input information data DT.sub.USE is supplied to an outer encoder 2. As shown in FIG. 4, this encoder generates, by the use of a predetermined polynomial with regard to the data blocks (each data block is comprised of 118 bytes of the input information data DT.sub.USE), outer codes which are parity codes RO.sub.0 -RO.sub.305. Each parity code RO is comprised of a 10-byte Reed-Solomon code and each such parity code is added to the end of each data block, which is thereafter provided as an outer data block DO. The outer data block DO is fed via a first multiplexer 3 to a memory unit 4. FIG. 5 shows the structure of the memory unit 4 and the data arrangement therein. As shown, the memory unit 4 is comprised of memories MEM1 and MEM2, each having a capacity of 154 bytes in a row and 128 bytes in a column. In this example, 153 outer data blocks DO.sub.0 -DO.sub.152 generated sequentially by outer encoder 2 are stored in the memory MEM1, while the next 153 outer data blocks DO.sub.153 -DO.sub.305 generated sequentially by the outer encoder following the outer data blocks DO.sub.0 -DO.sub.152 are stored in the memory MEM2 in such a manner that 1 outer data block is written per column. The information data of 1 outer data block is formed of 118 bytes and, since 153 blocks of information data are written in each of the memories MEM1 and MEM2, it follows that a total of 118.times.153.times.2 bytes (=36,108 bytes) of the information data are written in the memory unit 4.
The data writing direction in each column of the memories MEM1 and MEM2 is indicated by an arrow A in FIG. 5, and the lower 10 bytes in each column of the memories MEM1 and MEM2 correspond to the outer code.
There are also fed, via the first multiplexer 3 to the memory unit 4, data block identification data ID.sub.B generated from an identification data generator 5 for identifying the individual rows in the memories MEM1 and MEM2. Even components ID.sub.BE of such data block identification data ID.sub.B are written into a predetermined column of the memory MEM1 while odd components ID.sub.BD thereof are written into a predetermined column of the memory MEM2 in the direction A.
The data thus written in the memories MEM1 and MEM2 are read out therefrom in the direction B in such a manner that the data of each row is processed as one block. The data reading operation for individual rows is performed alternately, with respect to the memories MEM1 and MEM2, in the order conforming to the data block identification data ID.sub.B (00, 01, 02, 03, . . . ).
The data read out from the memories MEM1 and MEM2 is supplied to an inner encoder 6.
This encoder 6 generates, by the use of a predetermined polynomial with regard to each of the input data blocks, inner codes which are parity codes RI.sub.0 -RI.sub.255 each formed of an 8-byte Reed-Solomon code. As shown in FIG. 6, such parity codes are added to the ends of the data blocks respectively to form inner data blocks DI.sub.0 -DI.sub.255, which are then applied to a second multiplexer 7.
The second multiplexer 7 selectively produces at its output the preamble data PR and the postamble data PS formed by a preamble/postamble generator 8 on the one hand, and the inner data blocks DI.sub.0 -DI.sub.255 supplied from the inner encoder 6 on the other hand. Such data are produced in the following order: the preamble data PR, the inner data blocks DI.sub.0 -DI.sub.255 and the postamble data PS. The output for the second multiplexer 7 is fed to a data randomizer 9.
In the data randomizer 9, the data is randomized by taking an exclusive OR with regard to every byte of the input data and predetermined data. The data thus randomized is applied to an 8-9 modulator 10.
In this modulator 10, the form of the data is converted from 8-bit data to 9-bit data for the purpose of achieving a DC-free state by removal of the DC component from the signal waveform that will be recorded on the magnetic tape. Such conversion is performed in the following manner. With regard to each of 256 values of the input data where each byte is composed of 8 bits, two kinds of 9-bit data may be used in the ID-1 format to represent that 8-bit data. The codeword digital sums (CPS) of these two kinds of 9-bit data differ from each other in polarity. The 8-9 modulator 10 monitors the digital sum variation (DSV) of the 9-bit data produced from the input data and selects one or the other of the two kinds of 9-bit data such that the CDS value thereof reduces the DSV value to zero. Thus, input 8-bit data is converted into DC-free 9-bit data. The 8-9 modulator 10 includes a circuit for converting the input data of NRZL (non-return to zero level) form into that of NRZI (non-return to zero inverse) form. The 9-bit output data of the 8-9 modulator 10 in NRZI form is supplied to a third multiplexer 11.
In the third multiplexer 11, a sync code SNYC.sub.B of a fixed 4-byte length obtained from a sync code generator 12 is added to each of the inner data blocks DI.sub.0 -DI.sub.255, whereby sync blocks BLK.sub.0 -BLK.sub.255 are formed. The pattern of such sync code SYNC.sub.B is determined on the basis of the ID-1 format, and the pattern to be recorded on the magnetic tape is so prescribed as to conform with such code pattern.
The delta obtained in the above processes is shown in the form of maps in FIG. 7. The output of the third multiplexer 11 has a data array obtained by scanning such maps MAP1 and MAP2 in the horizontal direction. The further detail thereof is illustrated in FIG. 2. The output of the third multiplexer 11 is fed to a parallel-to-serial converter 13.
In the parallel-to-serial converter 13, the input parallel-bit data of preamble PR, sync blocks BLK.sub.0 -BLK.sub.255 and postamble PS is converted into serial-bit data S.sub.REC. Such serial data S.sub.REC is amplified by a record amplifier 14 and then is supplied as a record signal to a magnetic head 16 which scans the magnetic tape 15 in a helical scanning mode, whereby record tracks TR ( . . . , TR1, TR2, TR3, TR4, . . . ) are formed on the magnetic tape 15 as illustrated in FIG. 1.
In this manner, the recording system operates to add an error correction code, which is based on the Reed-Solomon product code notation, to the desired information data DT.sub.USE to be recorded.
The information data DT.sub.USE thus recorded on the magnetic tape 15 by the recording system of FIG. 3 is reproduced by a reproducing system illustrated in FIG. 8 which operates inversely to the operation performed by the recording system.
In this reproducing system, the record tracks TR ( . . . , TR1, TR2, TR3, TR4, . . . ) on the magnetic tape are reproduced by a magnetic head 16 as a playback signal S.sub.PB, which is then supplied to a playback amplifier 21.
The playback amplifier 21 includes an equalizer and a binary encoder, wherein playback digital data DT.sub.PB is obtained by encoding the input playback signal S.sub.PB in binary notation. This binary-encoded playback data DT.sub.PB then is supplied to a serial-to-parallel converter 22 for conversion into 9-bit parallel data DT.sub.PR.
In a sync code detector 23, the 4-byte sync code SYNC.sub.N is detected from a stream of parallel data DT.sub.PR, and the sync block is identified in accordance with the detected sync code. The sync code detector 23 includes a circuit for converting the NRZI-form parallel data DT.sub.PR into NRZL-form data.
The output of the sync code detector 23 is coupled to an 8-9 demodulator 24, where the data that had been processed by 8-to-9 bit conversion to be rendered DC-free in the recording system is demodulated to return to an 8-bit combination again. The demodulator 24 includes a ROM (read-only memory) and converts the 9-bit data to 8-bit data by a retrieval process compatible with the 8-9 bit conversion process.
The 8-bit data thus restored is derandomized in a derandomizer 25 through a process inverse to the randomization process executed in the recording system. Such derandomization is achieved by calculating the exclusive OR of the predetermined data used for the randomization and the input data fed to the derandomizer 25 from demodulator 24.
An inner code error detector/corrector 26 performs error detection and correction by using the 8-byte inner error code RI.sub.0 -RI.sub.255 that had been added to the inner data blocks DI.sub.0 -DI.sub.255, respectively, forming the sync blocks BLK.sub.0 -BLK.sub.255.
The inner data blocks DI.sub.0 -DI.sub.255 following inner code error correction are written in a memory unit 28, which is structurally the same as the aforementioned memory unit 4 of the recording system, shown in greater detail in FIG. 5, on the basis of the 1-byte block identification data ID.sub.B that had been added to each block and that is now detected by an identification data detector 27. Consequently, one data block is written in one row. The data writing order is the same as the order in which the data had been read out from the memory unit 4 in the recording system, and the data blocks DI.sub.0 -DI.sub.255 are written in the memories MEM1 and MEM2 row by row alternately in conformity with the block identification data. The data thus written into the rows of the memories MEM1 and MEM2 of the memory unit 28 are read out column by column in the same order as the data had been written into the columns of memory unit 4 of the recording system. Consequently, the 128-byte outer data blocks DO.sub.0 -DO.sub.305 are restored.
An outer code error detector/corrector 29 performs error detection and correction on the output data blocks DO.sub.0 -DO.sub.305 read from the memory unit 28, by using the 10-byte outer code RO.sub.0 -RO.sub.305 that had been added to the data blocks respectively.
Thus, the information data DT.sub.USE recorded on the magnetic tape 15 is reproduced in the manner described above.
In the information data recording/reproducing apparatus of the type just mentioned, the information data DT.sub.IN input successively in a recording mode is internally divided into individual sectors or tracks formed by the rotary magnetic head 16 in accordance with a recording pattern such as . . . , TR1, TR2, TR3, TR4, . . . (shown in FIG. 1). And in a playback mode, the divided data of the individual sectors are reproduced and combined with one another to be output as successive playback data DT.sub.OUT.
Accordingly, for assuring the proper phase relation in a playback mode with regard to the information data DT.sub.IN, sync data representing the phase relation of that information data DT.sub.IN is inserted into the information data DT.sub.IN before the information data is supplied to the recording section, and such sync data is used as a reference to attain exact replication of the phase relation during the playback mode.
Heretofore, when the sync data is recorded together with the information data DT.sub.IN on the magnetic tape, it is necessary to employ a different data pattern having a distinctive detectable characteristic in comparison with the information data DT.sub.IN. Consequently, in magnetic recording/reproducing apparatus designed to record arbitrary information data DT.sub.IN having an unpredictable bit pattern, in order to retain the unique distinctiveness of the sync data, the redundancy of the sync data is increased greatly.
Other techniques have been contemplated to reference the phase relation of the information data DT.sub.IN being recorded, including forming a blank portion in accordance with the phase relation of the: information data DT.sub.IN, or recording, together with the information data DT.sub.IN, additional data indicative of the beginning or end of the information data or indicative of the record block length. Various combinations of these techniques also have been proposed.
However, the foregoing generally are not successful because they are not easy to adopt, they consume useful data storage capacity due to their high redundancy, and they often are quite complex. Furthermore, even when these proposals for sync data have been used, the proper phase relation of the reproduced information data is not ensured if an error is generated due to dropout or the like on the magnetic tape.